In vitro "hemi-atrium" preparations from the elasmobranch skate heart and the amphibian marine toad that were previously developed in this laboratory will now be used to characterize taurine transport. Our emphasis on taurine enflux derives from earlier experiments by others that suggest an involvement with increased sympathomimetic activity that has general physiological and clinical significance. These in vitro preparations with no coronary circulation will beat for hours in an adequately buffered balanced isotonic medium. Hemi-atria from skates and toads mounted in "Ussing chambers" for special purposes also function very satisfactorily. Furthermore, single fibers can be mounted to measure action potential and contraction, and a spontaneous atrial beat will persist as long as 4 hours after the fiber is isolated, mounted and even when subjected to repeated experimentation. Comparative techniques will also be used to evaluate the hypothesis that the elevated taurine levels found in congestive failure are explained by a deficient taurine uptake or retention system that is maximally stimulated when in a stressed heart is in a state of chronic beta-activation. Developing hearts of chick embryos, before and after adrenergic innervation is established, will be compared and the hearts of elasmobranchs which are totally without an adrenergic innervation throughout life will be compared with related animals having dually innervated hearts. A link that has been suggested between beta-adrenergic stimulation of calcium fluxes and taurine transport will also be examined.